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#!/usr/bin/env python
#
#   Library:    pyflowctrl
#   Module:     hashfile1
#   Dependency:    core2
#   Examples:   examples/example14.py
#
#   links: Cryptographic hash function, http://en.wikipedia.org/wiki/Cryptographic_hash_function
#

import os
import hashlib
from core2 import Stream, Process, EmptyStream
from streams.stdiostreams1 import StandardErrorStream

class UnknownAlgorithm(Exception): pass

class FileHash(Process):
    ''' File hash calculation '''
    
    def __init__(self, algorithm='md5'):
        super(FileHash, self).__init__()
        self.io = { 
            'input': Stream(data_type='path'),
            'output': Stream(data_type=('path', 'hash')),
            'error': StandardErrorStream()
        }
        self.hashfunc = None
        if algorithm in hashlib.algorithms:
            # 'md5', 'sha1', 'sha224', 'sha256', 'sha384', 'sha512'
            if algorithm == 'md5':
                self.hashfunc = hashlib.md5
            elif algorithm == 'sha1':
                self.hashfunc = hashlib.sha1
            elif algorithm == 'sha224':
                self.hashfunc = hashlib.sha224
            elif algorithm == 'sha256':
                self.hashfunc = hashlib.sha256
            elif algorithm == 'sha384':
                self.hashfunc = hashlib.sha384
            elif algorithm == 'sha512':
                self.hashfunc = hashlib.sha512
        else:
            raise UnknowAlgorithm(algorithm)

    def hashcalc(self, path):
        ''' calculation of file hash '''
        try:
            data = open(path, 'rb')
            handler = self.hashfunc()
            chunk_size = 2**16 # chunk size of file
            while 1:
                chunk = data.read(chunk_size)
                if not chunk: break
                handler.update(chunk)
            data.close()
        except IOError:
            return None
        return handler.hexdigest()
            
    def main(self):
        while True:
            path = self.io['input'].get()
            if os.path.isfile(path):
                self.io['output'].put((path, self.hashcalc(path)))
            else:
                self.io['error'].put("%s is not a file\n" % path)
                continue
            yield